Neurogenesis persists in the dentate gyrus of all adult mammals, including humans. Neural production is perturbed by many physiological and pathological conditions, and selective manipulation of neurogenesis suggests that adult born neurons contribute to hippocampal-dependent behaviors. Despite growing knowledge of the cell biological processes directing neurogenesis, less is known about the physiological properties that may endow the small population of adult born neurons to contribute to hippocampal function. One possibility is that the continually renewing population of immature neurons exhibits distinct properties from the larger population of pre-existing neurons, resulting in unique functionality. Although considerable attention has focused on transient differences in intrinsic excitability, the potential consequences of distinct circuitry have not been explored. The goal of this project is to determine how changes in synaptic connectivity across maturation affect activation of dentate neurons, potentially allowing immature and mature neurons to process distinct components of hippocampal network activity. Dentate neurons receive two main excitatory afferent projections; the perforant path originating from the entorhinal cortex and the associational/commissural pathway arising from hilar mossy cells within the hippocampus itself. We will use in vitro slice physiology, a variety of transgenic mouse models and optogenetics to address how changing synaptic connectivity and intrinsic properties control recruitment at progressive stages of maturation. First we will focus on understanding the mechanisms controlling excitatory drive and synaptic integration of the perforant path and associational/commissural pathways (Aims 1 & 2).These single cell studies will be extended to test functional consequences of selective pathway stimulation at the synaptic and circuit level (Aim 3). We will go beyond circuit mapping to understand how stage-specific synaptic properties interact with intrinsic excitability to dictate integration of cortical and hippocampal afferent activity. Together the results of these Aims will reveal how synaptic connectivity contributes to the participation of immature neurons in dentate circuitry and provide insight into the potential for adult neurogenesis to produce a heterogeneous population of dentate neurons that can play diverse roles in hippocampal function. Understanding the physiological function of adult born neurons is an essential component of dissecting the significance and purpose of adult neurogenesis, a dramatic form of brain plasticity that may be a therapeutic target for numerous brain disorders.